Storms add concerns about pathogen threat to almonds
University of California researchers are warning almond growers to be on the look- out for a rare disease that can cause severe damage to their orchards. Phytophthora, soil-borne microorgan- isms described as “water molds” because of their dependence on water, can cause root and crown rot at the base of trees. The pathogens can also be carried through the air and attack upper branches. With heavy storms hitting California last week and more in the forecast this month, one species—phytophthora syringae— was drawing renewed attention. Last year, researchers said there was an unprecedented outbreak of the disease, fueled by the series of atmospheric river storm events that pounded California. According to a report this month from researchers at UC Davis and UC Riverside, the disease was discovered in Fresno County almond orchards last February and spread across the state by early summer. “It was found statewide, meaning in ev- ery almond-producing county, and dis- ease incidence in orchards ranged from 10% of the trees infected to 75%,” Florent Trouillas, a UC Cooperative Extension specialist in fruit and nut pathology, said in a statement.
Trouillas, UC Riverside plant patholo- gy professor Jim Adaskaveg and UC Davis graduate student Alejandro Hernandez published findings from research tracking the spread of the pathogen. Their report said almond orchards with severe outbreaks had numerous trees with branch dieback and cankers with profuse gumming in the upper scaffold branches. Infections often started on lateral shoots and progressed into major limbs or scaf- fold branches, where the abundant gum- ming was produced. Although the disease does not kill the tree, it causes branch dieback that requires significant additional work and expense for almond growers. During last year’s outbreak, researchers observed phytophthora syringae, known to attack the cuts caused by pruning. Researchers reported it was directly in- fecting the young shoots on almond trees without any wounds. Outbreaks of the pathogen have been associated with wet El Niño years, said Trouillas, who warned that growers state- wide should be on high alert for additional breakouts following rainstorms. He said almond growers who prune during winter months should aim to do
Gold, amber and burgundy gum balls on almond trees may be the result of phytophthora syringae. The pathogen spread widely during 2023 storms, and researchers warn growers to be on alert.
so in 10- to 14-day periods of dry weather. “If growers were to prune around a rain event—before, during or shortly after— this increases the likelihood of infection because this pathogen moves around with water,” Trouillas said. Starting around bloom time in mid-Feb- ruary, he said, growers should monitor
pruning wounds and young shoots on their trees. Gum balls, ranging from gold and amber to dark burgundy to bright red, could indicate infection. Trouilla added, “There are many oth- er diseases that can cause gumming on the tree.” He urged growers to contact their local Cooperative Extension advi- sor for confirmation.
April 9 - 11, 2024 | The Meritage Resort & Spa | Napa, CA
ANNOUNCING ANNUAL KEYNOTE SPEAKER
CHRIS BARTON Founder and Creator of Shazam, Entrepreneur, Inventor, and Tech Investor
REGISTER TODAY
UNITEDAGCONFERENCE.ORG
February 7, 2024 Ag Alert 9
Powered by FlippingBook